Summary of Significant Accounting Policies (Schedule of Revenue by Major Customers) (Details)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Genentech [Member] | Avastin [Member]
Entity Wide Revenue Major Customer [Line Items]
Percentage of total revenue (in Percent)	36.00%	30.00%
Genentech [Member] | Herceptin [Member]
Entity Wide Revenue Major Customer [Line Items]
Percentage of total revenue (in Percent)	33.00%	33.00%
Genentech [Member] | Lucentis [Member]
Entity Wide Revenue Major Customer [Line Items]
Percentage of total revenue (in Percent)	13.00%	14.00%
Elan [Member] | Tysabri [Member]
Entity Wide Revenue Major Customer [Line Items]
Percentage of total revenue (in Percent)	14.00%	15.00%